1. Field of the Invention
The present invention pertains to wireless telecommunications, and particularly to moveover or relocation of a serving radio network control node in a radio access network.
2. Related Art and other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified, typically by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which is in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a wideband code division multiple access (W-CDMA) system.
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed code, such as a pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
The Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN) accommodates both circuit switched and packet switched connections. In this regard, in UTRAN the circuit switched connections involve a radio network controller (RNC) communicating with a mobile switching center (MSC), which in turn is connected to a connection-oriented, external core network, which may be (for example) the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). On the other hand, in UTRAN the packet switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN) which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched networks (e.g., the Internet, X.25 external networks).
For the UMTS R99 standard as specified by the Third Generation Partnership Project (3GPP), AAL2/ATM was selected as the user data transport in the wideband CDMA (WCDMB) radio access network (e.g., the UTRAN). Asynchronous Transfer Mode (ATM) technology (ATM) is a packet-oriented transfer mode which uses asynchronous time division multiplexing techniques. Packets are called cells and have a fixed size. An ATM cell consists of 53 octets, five of which form a header and forty eight of which constitute a “payload” or information portion of the cell. The header of the ATM cell includes two quantities which are used to identify a connection in an ATM network over which the cell is to travel, particularly the VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). In general, the virtual path is a principal path defined between two switching nodes of the network; the virtual channel is one specific connection on the respective principal path.
A protocol reference model has been developed for illustrating layering of ATM. The protocol reference model layers include (from lower to higher layers) a physical layer (including both a physical medium sublayer and a transmission convergence sublayer), an ATM layer, and an ATM adaptation layer (AAL), and higher layers. The basic purpose of the AAL layer is to isolate the higher layers from specific characteristics of the ATM layer by mapping the higher-layer protocol data units (PDU) into the information field of the ATM cell and vise versa.
There are several differing AAL types or categories, including AAL0, AAL1, AAL2, AAL3/4, and AAL5. AAL2 is a standard defined by ITU recommendation 1.363.2. An AAL2 packet comprises a three octet packet header, as well as a packet payload. The AAL2 packet header includes an eight bit channel identifier (CID), a six bit length indicator (LI), a five bit User-to-User indicator (UUI), and five bits of header error control (HEC). The AAL2 packet payload, which carries user data, can vary from one to forty-five octets. Several AAL2 packets can be multiplexed on an ATM virtual channel (ATM VC).
The radio network controller (RNC) controls the UTRAN. In fulfilling its control role, the RNC manages resources of the UTRAN. Such resources managed by the RNC include (among others) the downlink (DL) power transmitted by the base stations; the uplink (UL) interference perceived by the base stations; and the hardware situated at the base stations.
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “Iub” interface. The interface between the user equipment unit (UE) and the base stations is known as the “air interface” or the “radio interface” or “Uu interface”. In some instances, a radio connection involves both a Serving or Source RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the radio connection but with one or more radio links of the radio connection being handling by the DRNC. An Inter-RNC transport link can be utilized for the transport of control and data signals between Source RNC and a Drift or Target RNC, and can be either a direct link or a logical link as described, for example, in International Application Number PCT/US94/12419 (International Publication Number WO 95/15665). An interface between radio network controllers (e.g., between a Serving RNC [SRNC] and a Drift RNC [DRNC]) is termed the “Iur” interface.
Those skilled in the art appreciate that, with respect to a certain RAN-UE connection, an RNC can either have the role of a serving RNC (SRNC) or the role of a drift RNC (DRNC). If an RNC is a serving RNC (SRNC), the RNC is in charge of the radio connection with the user equipment unit (UE), e.g., it has full control of the radio connection within the radio access network (RAN). A serving RNC (SRNC) is connected to the core network. On the other hand, if an RNC is a drift RNC (DRNC), its supports the serving RNC (SRNC) by supplying radio resources (within the cells controlled by the drift RNC (DRNC)) needed for the radio connection with the user equipment unit (UE). A system which includes the drift radio network controller (DRNC) and the base stations controlled over the Iub Interface by the drift radio network controller (DRNC) is herein referenced as a DRNC subsystem or DRNS.
When a radio connection between the radio access network (RAN) and user equipment unit (UE) is being established, the radio access network (RAN) decides which RNC is to be the serving RNC (SRNC) and, if needed, which RNC is to be a drift RNC (DRNC). Normally, the RNC that controls the cell where the user equipment unit (UE) is located when the radio connection is first established is initially selected as the serving RNC (SRNC). As the user equipment unit (UE) moves, the radio connection is maintained even though the user equipment unit (UE) may move into a new cell, possibly even a new cell controlled by another RNC. That other RNC becomes a drift RNCs (DRNC) for RAN-UE connection. An RNC is said to be the Controlling RNC (CRNC) for the base stations connected to it by an Iub interface. This CRNC role is not UE specific. The CRNC is, among other things, responsible for handling radio resource management for the cells in the base stations connected to it by the Iub interface.
In certain situations it its advantageous to transfer control of a particular UE connection from one RNC to another RNC. Such a transfer of control of the UE connection from one RNC to another RNC has been referred to as soft RNC handover, SRNC moveover, and SRNC relocation. A relocate function/procedure is provided to effect this transfer of control. This is a general function/procedure covering UMTS internal relocations (e.g., relocation of SNRC within the UMTS) as well as relocations to other systems (e.g., from UMTS to GSM, for example). SRNC relocation is described in various references, including the following example commonly assigned patent applications (all of which are incorporated herein by reference):
(1) U.S. patent application Ser. No. 09/035,821 filed Mar. 6, 1998, entitled “Telecommunications Inter-Exchange Measurement Transfer”;
(2) U.S. patent application Ser. No. 09/035,788 filed Mar. 6, 1998, entitled “Telecommunications Inter-Exchange Congestion Control”;
(3) U.S. patent application Ser. No. 08/979,866 filed Nov. 26, 1997, entitled “Multistage Diversity Handling For CDMA Mobile Telecommunications”;
(4) U.S. patent application Ser. No. 08/980,013 filed Nov. 26, 1997, entitled “Diversity Handling Moveover For CDMA Mobile Telecommunications”;
(5) U.S. patent application Ser. No. 09/732,877 filed Dec. 11, 2000, entitled “Control Node Handover In Radio Access Network”;
(6) U.S. patent application Ser. No. 09/543,536 filed Apr. 5, 2000, entitled “Relocation of Serving Radio Network Controller With Signaling of Linking of Dedicated Transport Channels”.
SRNC relocation is intended to make more efficient use of the transmission network. Once the former SRNC is not needed, the connection to the core network is moved and the connection between the two RNCs (the former SRNC and the former DRNC over the Inter-RNC link) is disconnected.
An important function in the new CDMA networks is the soft handover function (briefly described above). Implementation of soft handover is facilitated by a diversity handling (DHO) unit or device. The DHO is situated at the SRNC handling the connection to a certain user equipment unit (UE). In the uplink from the user equipment unit (UE), the DHO combines the user data from two or more legs from different base stations, choosing the best data for forwarding on to the other party involved in the connection. In the downlink, the DHO splits the data into two or more legs for transmission to the different base stations. A DHO is always involved in a connection which has soft handover capability.
As mentioned above, a DHO is allocated in the SRNC. FIG. 1 shows such a SRNC 3261 connected to a core network and controlling radio base stations RBS 3281-1 through RBS 3282-1. The SRNC 3261 has a DHO 3271, as well as an extension terminal ET 3251 through which SRNC 3261 interfaces with Inter-RNC link 329. FIG. 1 further shows a DRNC 3262, having an extension terminal ET 3252-1 for interfacing with the Inter-RNC link, and controlling radio base stations RES 3282-1 through RBS 3282-2. FIG. 1 shows a situation having a call involving user equipment unit (UE) 330 routed over DRNC 3262, with a DHO 3272, also being allocated at the DRNC 3262 just in case SRNC relocation should occur (e.g., pending SRNC relocation). But this allocation of an extra DHO exacts network resources, and can introduce an undesired delay.
Rather than a situation involving two allocated DHOs such as that shown in FIG. 1, it is more preferable that only one DHO be allocated at a time for a given connection, with that one DHO being at the SRNC. To cater to this preference, it is conceivable to wait to allocate a new DHO 3272 at a new SRNC 3262 until the SRNC relocation actually occurs as shown in FIG. 2, and to set up a new connection from the DHO to the RBS after disconnecting the old connection. The connections are then always setup end-to-end by means of AAL2 signaling. However, the applicable standards require that the connection to the RBS from the DRNC always be kept.
What is needed, therefore, and an object of the present invention, is a SRNC relcoation technique which involves allocation of only one diversity handling unit (DHO) at a time, but which does not change the connection from the new SRNC to the radio base station (RBS).